The present invention relates to a method and apparatus for treating tobacco, and more particularly to a method and apparatus for converting particles or fragments of tobacco into a continuous tobacco stream, for example, into a stream which is ready for trimming and conversion into a wrapped cigarette rod. Still more particularly, the invention relates to improvements in a method and apparatus for building a tobacco stream from a plurality of different types of tobacco, particularly from tobacco shreds and so-called short tobacco. The term "short tobacco" is intended to embrace tobacco dust as well as fragments which are removed from an unequalized tobacco stream by a cutting action during conversion of such stream into a trimmed stream or filler which is ready for wrapping into cigarette paper, imitation cork or other suitable wrapping material.
It is already known to build a tobacco stream from freshly supplied tobacco shreds which are withdrawn from a first magazine and are mixed with short tobacco, i.e., with tobacco which is removed from an unequalized stream by trimming and is returned to the distributor of the stream forming machine, e.g., of a cigarette maker. It is also known to place the magazine for accumulated short tobacco upstream of the magazine for freshly supplied tobacco shreds and to employ a suitable conveyor which is provided with spaced-apart entraining elements in the form of vanes or blades capable of removing batches of short tobacco from the upstream magazine and thereupon tobacco shreds from the downstream magazine. Reference may be had to commonly owned U.S. Pat. No. 4,185,644 granted Jan. 29, 1980 to Heitmann et al. The conveyor of Heitmann et al. is an endless elevator having an elongated upwardly moving stretch whose vanes move first past the upstream magazine for short tobacco and thereupon past the downstream magazine for fresh tobacco shreds. A paddle wheel equalizes the accumulated tobacco batches, each of which contains short tobacco as well as tobacco shreds, before the batches are dumped into an upright duct for conversion into a continuous stream which contains a surplus of tobacco. The stream is then trimmed by removing the surplus therefrom whereby the removed surplus constitutes or forms part of short tobacco. A suitable conveyor system, e.g., a pneumatic conveyor or a combination of pneumatic and mechanical conveyors, is utilized to transport short tobacco from the trimming station to the magazine which is adjacent to the upwardly moving reach of the aforementioned endless elevator. As a rule, the magazine which serves for storage of freshly supplied tobacco shreds also contains some particles of stem, ribs, birds' eyes and like relatively hard and often bulky fragments of tobacco which should be segregated from other particles prior to the trimming and wrapping steps. To this end, the duct which receives batches of tobacco from the vanes of the endless elevator is normally followed by a classifying unit which segregates particles of ribs, stem and the like from satisfactory particles before the satisfactory particles are converted into a stream which is advanced toward and past the trimming device or devices. The quality of the distributor (i.e., of that part of a cigarette making or an analogous machine which delivers tobacco particles to the stream forming or stream building station) greatly affects the quality of the ultimate product. Thus, a satisfactory distributor must form a uniform or nearly uniform tobacco stream with a minimum of short tobacco because the latter is inferior to freshly supplied tobacco shreds and is reprocessed primarily because of the high cost of tobacco, i.e., the manufacturers of cigarettes strive to use up all or nearly all parts of tobacco leaves including laminae as well as ribs, stem and relatively small fragments (short tobacco) which necessarily develop in the course of processing (especially trimming) in a cigarette making machine. Furthermore, the quality of cigarettes is more satisfactory if the percentage of short tobacco in each of a long series of cigarettes is uniform, i.e., if the quantity of short tobacco does not fluctuate extensively from cigarette to cigarette or from cigarette pack to cigarette pack.
Commonly owned German Offenlegungsschrift No. 27 29 730 discloses a distributor wherein short tobacco which develops as a result of trimming a continuous tobacco stream is reprocessed without delay and without permitting such tobacco to mix with freshly supplied tobacco shreds. Moreover, such short tobacco is prevented from accumulating into a large mass prior to reintroduction into the stream building zone. It has been found that such distributors are quite satisfactory in many respects with the important exception that the quantity or percentage of short tobacco is likely to vary from cigarette to cigarette or from a relatively short first series to the next-following series of cigarettes.